I used to play with fire and didn't learn my lesson until I set the yard on fire one dry summer. It has to get personal before he learns a true lesson. Either by getting burned or by a fire getting out of control. There is very little you can do aside from limiting his access to lighters and matches until he grows out of this.
He may be picking up some of this off the internet. Playing with fire videos are showing up all over. There are a ton on YouTube...
https://youtube.com/results?search=fi...=search_videos